Shaped carbon articles are conventionally produced by mixing powdered carbon with a carbonaceous binder and forming the mixture into a green compact. The carbon may be present in the form of petroleum coke, coal coke, pitch coke, powdered graphite, carbon flour, and the like. The carbonaceous binder is tar or pitch derived from either petroleum or coal. These binders range from semi-liquid tars to solid pitches of high melting point.
After a green compact composition has been formed it is heated slowly to carbonize the binder. The greater the yield of carbon from the binder, the greater is the strength of the resulting bond between the carbon particles of the baked compact and the higher is the density.
High density and strength are particularly important when baked carbon articles are subsequently graphitized by high temperature treatment. To reduce porosity and increase strength, the shaped carbonaceous article is often impregnated with pitch and then recarbonized.
During the carbonizing process volatile material is driven off from the carbonaceous binder. At baking temperatures a scission of chemical bonds occurs, and some lighter constituents are formed and volatilized. Products of high molecular weight are generated by polymerization reactions. The greater the loss of volatile material during the carbonization process, the lower the strength and density of the final shaped carbon article. A variety of methods have been developed for reducing the quantity of volatile material lost during baking of a shaped carbon article, and for increasing the coking value of the binder component of a shaped carbon article.
U.S. Pat. No. 2,500,208 describes a reactive binder composition of high coking propensity consisting of a pitch containing a nitro aromatic additive.
U.S. Pat. No. 2,864,760 describes a method of improving the binding coke capacity of a coal tar binder pitch by pre-treating the binder pitch with a heavy metal chloride at a temperature of 150.degree. C.-200.degree. C.
U.S. Pat. No. 2,980,633 recommends the incorporation of an organo-metallic compound into green carbonaceous formulations for production of improved electrode type carbon articles.
U.S. Pat. No. 3,171,816 discloses a process for fabrication of carbon bodies with a mixture of granular coke, binder pitch, and an organic additive for reducing the binder softening point selected from unsaturated derivatives such as olefins, acetylenes, ketones, nitriles, and the like.
U.S. Pat. No. 3,280,042 proposes the inclusion of iron or aluminum chloride into a green mix to produce an improved graphite electrode.
Zinc chloride is known as a polymerization agent for increasing the carbon yield of an electrode binder. U.S. Pat. No. 3,505,090 suggests that some of the disadvantages of zinc chloride as an additive in green compact carbon formulations can be overcome by employing zinc chloride in the form of a complex with an organic amine compound.
There remains a need for novel green compact carbon formulations for production of electrodes and other shaped carbon articles which have improved mechanical and electrical properties.
Accordingly, it is an object of this invention to provide a green mix formulation which is adapted to produce baked carbon articles of high density and high compressive strength.
It is another object of this invention to provide a pre-bake electrode composition which includes a novel additive for increasing the binding coke capacity of the binder pitch component.
It is a further object of this invention to provide a carbon electrode which has a lower electrode consumption rate in aluminum electrolysis reactors than conventional carbon electrodes.
Other objects and advantages of the present invention shall become apparent from the accompanying description and exemplary data.